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Merge branch 'main' into feature/transaction-entry-order-and-month-activity
2 parents 364f7d0 + 1d867c5 commit 4222109

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Lines changed: 2403 additions & 43 deletions

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‎CompoundCalc/Models/Requests/CarLoanRequest.cs‎

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using System.ComponentModel.DataAnnotations;
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namespace CompoundCalc.Models.Requests;
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public sealed class CarLoanRequest
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{
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public CarLoanRequest(
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decimal vehiclePrice,
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decimal cashDownPayment,
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decimal tradeInValue,
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decimal tradeInPayoff,
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decimal annualRatePercent,
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int termMonths,
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decimal? salesTaxPercent,
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decimal? salesTaxAmount,
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decimal fees,
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decimal rebate,
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decimal financedExtras)
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{
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VehiclePrice = vehiclePrice;
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CashDownPayment = cashDownPayment;
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TradeInValue = tradeInValue;
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TradeInPayoff = tradeInPayoff;
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AnnualRatePercent = annualRatePercent;
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TermMonths = termMonths;
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SalesTaxPercent = salesTaxPercent;
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SalesTaxAmount = salesTaxAmount;
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Fees = fees;
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Rebate = rebate;
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FinancedExtras = financedExtras;
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Validate();
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}
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[Required] public decimal VehiclePrice { get; }
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[Required] public decimal CashDownPayment { get; }
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[Required] public decimal TradeInValue { get; }
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[Required] public decimal TradeInPayoff { get; }
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[Required] public decimal AnnualRatePercent { get; }
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[Required] public int TermMonths { get; }
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public decimal? SalesTaxPercent { get; }
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public decimal? SalesTaxAmount { get; }
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public decimal Fees { get; }
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public decimal Rebate { get; }
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public decimal FinancedExtras { get; }
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private void Validate()
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{
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if (VehiclePrice <= 0m)
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{
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throw new ArgumentOutOfRangeException(nameof(VehiclePrice), "Vehicle price must be greater than zero.");
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}
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if (CashDownPayment < 0m)
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{
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throw new ArgumentOutOfRangeException(nameof(CashDownPayment), "Cash down payment cannot be negative.");
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}
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if (TradeInValue < 0m)
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{
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throw new ArgumentOutOfRangeException(nameof(TradeInValue), "Trade-in value cannot be negative.");
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}
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if (TradeInPayoff < 0m)
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{
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throw new ArgumentOutOfRangeException(nameof(TradeInPayoff), "Trade-in payoff cannot be negative.");
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}
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if (AnnualRatePercent < 0m || AnnualRatePercent > 100m)
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{
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throw new ArgumentOutOfRangeException(nameof(AnnualRatePercent), "Annual rate percent must be between 0 and 100.");
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}
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if (TermMonths is < 1 or > 96)
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{
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throw new ArgumentOutOfRangeException(nameof(TermMonths), "Term months must be between 1 and 96.");
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}
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if (SalesTaxPercent is < 0m or > 100m)
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{
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throw new ArgumentOutOfRangeException(nameof(SalesTaxPercent), "Sales tax percent must be between 0 and 100.");
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}
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if (SalesTaxAmount is < 0m)
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{
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throw new ArgumentOutOfRangeException(nameof(SalesTaxAmount), "Sales tax amount cannot be negative.");
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}
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if (Fees < 0m)
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{
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throw new ArgumentOutOfRangeException(nameof(Fees), "Fees cannot be negative.");
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}
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if (Rebate < 0m)
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{
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throw new ArgumentOutOfRangeException(nameof(Rebate), "Rebate cannot be negative.");
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}
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if (FinancedExtras < 0m)
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{
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throw new ArgumentOutOfRangeException(nameof(FinancedExtras), "Financed extras cannot be negative.");
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}
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if ((SalesTaxPercent.HasValue && SalesTaxAmount.HasValue) || (!SalesTaxPercent.HasValue && !SalesTaxAmount.HasValue))
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{
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throw new ArgumentException("Provide either sales tax percent or sales tax amount.");
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}
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}
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}

‎CompoundCalc/Models/Responses/CarLoanResult.cs‎

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namespace CompoundCalc.Models.Responses;
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public sealed record CarLoanAmortizationEntry(
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int Month,
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decimal Payment,
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decimal Principal,
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decimal Interest,
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decimal RemainingBalance);
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public sealed record CarLoanResult(
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decimal VehiclePrice,
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decimal CashDownPayment,
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decimal TradeInValue,
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decimal TradeInPayoff,
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decimal NetTradeInCredit,
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decimal TotalUpfrontCredit,
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decimal SalesTax,
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decimal Fees,
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decimal Rebate,
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decimal FinancedExtras,
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decimal AmountFinanced,
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decimal AnnualRatePercent,
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int TermMonths,
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decimal MonthlyPayment,
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decimal TotalPaid,
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decimal TotalInterest,
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string AmountFinancedDisplay,
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string MonthlyPaymentDisplay,
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string TotalPaidDisplay,
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string TotalInterestDisplay,
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string TotalUpfrontCreditDisplay,
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string NetTradeInCreditDisplay,
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string CalculationVersion,
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IReadOnlyList<CarLoanAmortizationEntry> AmortizationSchedule)
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{
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public static CarLoanResult Create(
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decimal vehiclePrice,
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decimal cashDownPayment,
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decimal tradeInValue,
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decimal tradeInPayoff,
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decimal netTradeInCredit,
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decimal totalUpfrontCredit,
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decimal salesTax,
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decimal fees,
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decimal rebate,
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decimal financedExtras,
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decimal amountFinanced,
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decimal annualRatePercent,
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int termMonths,
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decimal monthlyPayment,
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decimal totalPaid,
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decimal totalInterest,
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IReadOnlyList<CarLoanAmortizationEntry> amortizationSchedule,
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Func<decimal, string> currencyFormatter,
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string calculationVersion)
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{
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var roundedAmountFinanced = Math.Round(amountFinanced, 2, MidpointRounding.ToEven);
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var roundedMonthlyPayment = Math.Round(monthlyPayment, 2, MidpointRounding.ToEven);
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var roundedTotalPaid = Math.Round(totalPaid, 2, MidpointRounding.ToEven);
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var roundedTotalInterest = Math.Round(totalInterest, 2, MidpointRounding.ToEven);
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var roundedTotalUpfrontCredit = Math.Round(totalUpfrontCredit, 2, MidpointRounding.ToEven);
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var roundedNetTradeInCredit = Math.Round(netTradeInCredit, 2, MidpointRounding.ToEven);
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return new CarLoanResult(
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VehiclePrice: vehiclePrice,
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CashDownPayment: cashDownPayment,
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TradeInValue: tradeInValue,
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TradeInPayoff: tradeInPayoff,
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NetTradeInCredit: roundedNetTradeInCredit,
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TotalUpfrontCredit: roundedTotalUpfrontCredit,
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SalesTax: Math.Round(salesTax, 2, MidpointRounding.ToEven),
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Fees: Math.Round(fees, 2, MidpointRounding.ToEven),
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Rebate: Math.Round(rebate, 2, MidpointRounding.ToEven),
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FinancedExtras: Math.Round(financedExtras, 2, MidpointRounding.ToEven),
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AmountFinanced: roundedAmountFinanced,
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AnnualRatePercent: annualRatePercent,
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TermMonths: termMonths,
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MonthlyPayment: roundedMonthlyPayment,
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TotalPaid: roundedTotalPaid,
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TotalInterest: roundedTotalInterest,
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AmountFinancedDisplay: currencyFormatter(roundedAmountFinanced),
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MonthlyPaymentDisplay: currencyFormatter(roundedMonthlyPayment),
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TotalPaidDisplay: currencyFormatter(roundedTotalPaid),
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TotalInterestDisplay: currencyFormatter(roundedTotalInterest),
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TotalUpfrontCreditDisplay: currencyFormatter(roundedTotalUpfrontCredit),
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NetTradeInCreditDisplay: currencyFormatter(roundedNetTradeInCredit),
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CalculationVersion: calculationVersion,
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AmortizationSchedule: amortizationSchedule);
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}
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}

‎CompoundCalc/Services/CalculationService.cs‎

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@@ -126,6 +126,46 @@ public MortgageResult CalculateMortgageEstimate(MortgageRequest request)
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calculationVersion: DefaultCalculationVersion);
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}
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public CarLoanResult CalculateCarLoanEstimate(CarLoanRequest request)
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{
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ArgumentNullException.ThrowIfNull(request);
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var netTradeInCredit = Math.Max(request.TradeInValue - request.TradeInPayoff, 0m);
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var totalUpfrontCredit = request.CashDownPayment + netTradeInCredit;
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var taxableBase = request.VehiclePrice;
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var salesTax = request.SalesTaxAmount ?? (taxableBase * (request.SalesTaxPercent!.Value / 100m));
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var preCreditTotal = request.VehiclePrice + salesTax + request.Fees + request.FinancedExtras - request.Rebate;
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var amountFinanced = Math.Max(preCreditTotal - totalUpfrontCredit, 0m);
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var monthlyRate = decimal.Divide(Conversions.ConvertPercentageToDecimal(request.AnnualRatePercent), 12m);
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var monthlyPayment = CalculateMonthlyMortgagePayment(amountFinanced, monthlyRate, request.TermMonths);
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var amortization = BuildAmortizationSchedule(amountFinanced, monthlyRate, request.TermMonths, monthlyPayment);
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var totalPaid = amortization.Sum(x => x.Payment);
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var totalInterest = amortization.Sum(x => x.Interest);
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return CarLoanResult.Create(
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vehiclePrice: request.VehiclePrice,
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cashDownPayment: request.CashDownPayment,
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tradeInValue: request.TradeInValue,
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tradeInPayoff: request.TradeInPayoff,
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netTradeInCredit: netTradeInCredit,
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totalUpfrontCredit: totalUpfrontCredit,
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salesTax: salesTax,
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fees: request.Fees,
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rebate: request.Rebate,
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financedExtras: request.FinancedExtras,
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amountFinanced: amountFinanced,
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annualRatePercent: request.AnnualRatePercent,
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termMonths: request.TermMonths,
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monthlyPayment: monthlyPayment,
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totalPaid: totalPaid,
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totalInterest: totalInterest,
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amortizationSchedule: amortization,
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currencyFormatter: Conversions.ConvertDecimalToCurrency,
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calculationVersion: DefaultCalculationVersion);
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}
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129169
private static CalculationResult RunCalculation(
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decimal principal,
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decimal annualRatePercent,
@@ -201,4 +241,38 @@ private static decimal CalculateMonthlyMortgagePayment(decimal principal, decima
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202242
return decimal.Divide(principal * monthlyRate, denominator);
203243
}
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private static IReadOnlyList<CarLoanAmortizationEntry> BuildAmortizationSchedule(
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decimal principal,
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decimal monthlyRate,
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int termMonths,
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decimal scheduledPayment)
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{
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var schedule = new List<CarLoanAmortizationEntry>(termMonths);
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var remainingBalance = principal;
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for (var month = 1; month <= termMonths; month++)
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{
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if (remainingBalance <= 0m)
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{
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break;
259+
}
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261+
var interest = monthlyRate > 0m
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? decimal.Round(remainingBalance * monthlyRate, 10, MidpointRounding.ToEven)
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: 0m;
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var payment = Math.Min(scheduledPayment, remainingBalance + interest);
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var principalPaid = payment - interest;
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remainingBalance = decimal.Round(Math.Max(remainingBalance - principalPaid, 0m), 10, MidpointRounding.ToEven);
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schedule.Add(new CarLoanAmortizationEntry(
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Month: month,
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Payment: decimal.Round(payment, 2, MidpointRounding.ToEven),
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Principal: decimal.Round(principalPaid, 2, MidpointRounding.ToEven),
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Interest: decimal.Round(interest, 2, MidpointRounding.ToEven),
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RemainingBalance: decimal.Round(remainingBalance, 2, MidpointRounding.ToEven)));
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}
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return schedule;
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}
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}

‎CompoundCalc/Services/Contracts/ICalculationService.cs‎

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@@ -9,4 +9,5 @@ public interface ICalculationService
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CalculationResult CalculateSavingsGrowth(SavingsCalcReq request);
1010
DebtPayoffResult CalculateDebtPayoff(DebtPayoffRequest request);
1111
MortgageResult CalculateMortgageEstimate(MortgageRequest request);
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CarLoanResult CalculateCarLoanEstimate(CarLoanRequest request);
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}

‎CompoundInterestCalculatorTests/Integration/CarLoanControllerTests.cs‎

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using System.Net;
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using System.Net.Http.Json;
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using Microsoft.AspNetCore.Mvc;
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using Microsoft.AspNetCore.Mvc.Testing;
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namespace CompoundInterestCalculatorTests.Integration;
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public class CarLoanControllerTests : IClassFixture<WebApplicationFactory<Program>>
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{
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private readonly WebApplicationFactory<Program> _factory;
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public CarLoanControllerTests(WebApplicationFactory<Program> factory)
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{
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_factory = factory;
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}
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[Fact]
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public async Task CarLoanEstimate_ReturnsPaymentTotalsAndAmortization()
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{
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var client = _factory.CreateClient();
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var request = new
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{
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vehiclePrice = 35000m,
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cashDownPayment = 3000m,
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tradeInValue = 8000m,
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tradeInPayoff = 5000m,
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annualRatePercent = 6.5m,
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termMonths = 60,
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salesTaxPercent = 7.5m,
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fees = 1200m,
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rebate = 1000m,
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financedExtras = 500m
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};
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var response = await client.PostAsJsonAsync("/api/v1/car-loan/estimate", request);
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Assert.Equal(HttpStatusCode.OK, response.StatusCode);
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var payload = await response.Content.ReadFromJsonAsync<CarLoanEstimateResponse>();
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Assert.NotNull(payload);
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Assert.Equal(6000m, payload!.totalUpfrontCredit);
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Assert.Equal(32325m, payload.amountFinanced);
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Assert.Equal(632.48m, payload.monthlyPayment);
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Assert.Equal(37948.80m, payload.totalPaid);
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Assert.Equal(5623.55m, payload.totalInterest);
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Assert.Equal(60, payload.amortizationSchedule.Count);
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Assert.False(string.IsNullOrWhiteSpace(payload.traceId));
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}
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[Fact]
52+
public async Task CarLoanEstimate_WhenTaxNotSpecified_ReturnsValidationProblem()
53+
{
54+
var client = _factory.CreateClient();
55+
56+
var request = new
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{
58+
vehiclePrice = 35000m,
59+
cashDownPayment = 3000m,
60+
tradeInValue = 8000m,
61+
tradeInPayoff = 5000m,
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annualRatePercent = 6.5m,
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termMonths = 60,
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fees = 1200m,
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rebate = 1000m,
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financedExtras = 500m
67+
};
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69+
var response = await client.PostAsJsonAsync("/api/v1/car-loan/estimate", request);
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Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
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var problem = await response.Content.ReadFromJsonAsync<ValidationProblemDetails>();
74+
Assert.NotNull(problem);
75+
}
76+
77+
private sealed record CarLoanEstimateResponse(
78+
decimal totalUpfrontCredit,
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decimal amountFinanced,
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decimal monthlyPayment,
81+
decimal totalPaid,
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decimal totalInterest,
83+
string traceId,
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IReadOnlyList<CarLoanAmortizationEntryResponse> amortizationSchedule);
85+
86+
private sealed record CarLoanAmortizationEntryResponse(
87+
int month,
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decimal payment,
89+
decimal principal,
90+
decimal interest,
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decimal remainingBalance);
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}

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